1. Technological Field
This invention is generally concerned with the control of electromagnetic interference and related problems associated with the operation of functional modules in electronic equipment enclosures. More particularly, embodiments of the invention relate to an electromagnetic radiation containment system that includes features directed to the containment and control of electromagnetic radiation associated with the operation of one or more functional modules arranged in an electrical equipment enclosure, and thereby contributes to a relative decrease in the EMI that may otherwise result from such operation.
2. Related Technology
Electronic equipment enclosures are used in a variety of different industries and applications and generally serve to receive one or more pieces of electronic equipment and devices in such a way that the pieces of electronic equipment can operably interact with each other and/or with the electronic equipment enclosure. In particular, such electronic equipment enclosures typically include features directed to permitting the use of one or more “plug-in” functional modules that electrically and mechanically interface with the electronic equipment enclosure and/or with other functional modules, and that can be removed and/or replaced as desired.
To this end, many electronic equipment enclosures include internal structures configured to removably receive one or more functional modules in a desired arrangement. Such internal structures are often referred to as “card cages.” The card cage is configured so as to allow a user to modify the functionality associated with the electronic equipment enclosure by selecting particular functional modules to be employed in the electronic equipment enclosure. Specifically, the functionality associated with a particular electronic equipment enclosure can be modified by adding and/or removing selected functional modules having desired functional aspects to/from the card cage. In this regard, many electronic equipment enclosures are configured so that they need not be fully occupied with functional modules in order for the functional modules to be operable. Rather, as few as one functional module can be operably employed in such electronic equipment enclosure configurations.
As suggested earlier, the functionality of any particular functional module or group of functional modules may vary widely according to the demands of a particular application. While their respective functionalities may differ however, many of such functional modules nonetheless share a number of similar structural features.
For example, typical functional modules employed in conjunction with card cages include a printed circuit board, or “card,” attached to a front panel that may include various indicators, readouts, and/or connectors. Circuitry disposed on the card communicates with such indicators, readouts and connectors and serves to implement the functionality associated with that particular functional module. Various connectors on the rear of the card permit communication between the functional module and other functional modules or components associated with the electronic equipment enclosure. Finally, the front panel of the functional module typically includes one or more fasteners that engage corresponding structure of the card cage to aid in removable retention of the functional module within the card cage.
While functional modules such as those just described have proven useful in many regards, they nevertheless suffer from certain limitations. One area of particular concern relates to the electromagnetic emissions or radiation generated by circuitry of the functional modules during the normal course of operations. Such radiation often produces various undesirable effects. For example, unchecked electromagnetic emissions may interfere with, and significantly impair, the operation and integrity of unshielded equipment and systems in the vicinity of the electronic equipment enclosure wherein the radiating functional module is employed. Effects such as these are considered in terms of the degradation or impairment of the performance of a particular device, equipment, or system as a result of an electromagnetic disturbance, and are often referred to as electromagnetic interference, or “EMI.”
Generally, EMI in a system/component occurs as a result of the generation and transmission of electromagnetic radiation by a radiation source such as a digital circuit of a functional module. EMI resulting from such emitted electromagnetic radiation can thus occur whenever a coupling path is established between a radiation source and unshielded systems/components in the vicinity of the radiation source. The coupling path can take a variety of forms. For example, the coupling path may comprise an electromagnetic or inductive coupling between the electromagnetic radiation source and the system/component where the EMI occurs
In yet other cases, the coupling path may comprise an electrically conductive path between the electromagnetic radiation source and the impacted system/component. In this case, electromagnetic radiation generated by the electromagnetic radiation source is electrically conducted to the system/component at the other end of the coupling path. Frequently, transmission of electromagnetic radiation by this mode is a result of ungrounded, or poorly grounded, radiation emitting circuitry and/or related connectors.
As the foregoing makes clear, unchecked electromagnetic emissions from functional modules in an electronic equipment enclosure can materially impair the integrity and performance of systems and equipment that happen to form a coupling path with one or more of the functional modules. Moreover, even if no significant EMI ultimately results from the operation of a functional module or other component, many types of electronic equipment, including functional modules, are nonetheless required to comply with permissible EMI limits specified in standards mandated by governmental authorities and regulatory bodies such as the Federal Communications Commission (“FCC”).
Because eliminating electromagnetic radiation emissions is impractical in many cases, at least one approach to resolving concerns such as those just described is to attempt to simply confine the emitted radiation in an effort to reduce the attendant EMI. Control of EMI in this way can be achieved to some extent by enclosing the system in a grounded conductive enclosure and by reducing the size of openings on the exterior of the enclosure so as to minimize the escape of electromagnetic radiation, such as would cause EMI, from the electronics contained within electronic equipment enclosure. Because the card cage defines a large opening in the enclosure, the front panels of the installed functional modules are required to complete the EMI containment of the enclosure.
A functional module completes the EMI containment by creating a low resistance conductive path between the front panel of the functional module and the front panels of adjacent functional modules and the surrounding enclosure. Unused card slots are typically filled with blank panels which incorporate the same EMI control features as a functional module and thus serve to complete the EMI containment of the enclosure.
For example, in many conventional electronic equipment enclosures and related systems and components, the short edges of the front panel of a functional module include conductive flanges which overlap the card cage mounting rails. This type of arrangement limits the flexibility of the card cage. In particular, the flanges of such functional modules are arranged to be connected to the rails of the card guide by an arrangement of screws and resilient elements that is intended to ensure good electrical contact between the functional module and the equipment enclosure. The vertical mounting configuration prevents horizontally adjacent card slots from being combined into a double wide or larger slot and, thus, the equipment enclosure is constrained for use solely with vertically stacked arrangements of horizontally oriented functional modules.
One consequence of this implementation of a functional module is that electrical communication between adjacent functional modules of this type, such as would aid in the containment of electromagnetic emissions, is only required to be implemented by conductive structures located on the top and bottom edges of the front panel of the functional module. To this end, some functional modules include electrically conductive “fingers” or other conductive elements, such as an EMI strip or gasket, that are configured and arranged to engage the conductive flange of the front panel of an adjacent functional module located above or below.
That is, functional modules of this type typically include a conductive flange along one long edge, and conductive fingers or similar conductive element along the other long edge, so that a conductive flange of one functional module contacts the conductive fingers of an adjacent functional module located above or below. Additional conductive fingers or gaskets may be employed to improve the electrical connection between the end flanges of the functional module front panel and the mounting rails. This arrangement of flanges and fingers is somewhat complex however and serves to complicate the manufacturing process. Moreover, this functional module configuration requires that the card cage include conductive fingers, either at the top or bottom of the opening, arranged to engage the flange of an installed functional module.
Thus, the configuration and arrangement of the card cage is largely dictated by the configuration of the functional modules to be used in that card cage and, in any event, is limited to use in connection with stacked arrangements of horizontally oriented functional modules, as discussed earlier. In particular, if a given functional module includes a conductive flange on the bottom edge, the corresponding electronic equipment enclosure must necessarily include conductive fingers, or similar structures, along the bottom that are able to interface with the flange of the functional module.
In general, the functionality of such conductive fingers or other conductive elements is sharply constrained by the fact that typical functional modules lack flexibility in terms of the configurations in which they may be arranged within the card cage of the electronic equipment enclosure.
In view of the foregoing, and other problems in the art not specifically enumerated herein, what is needed are electromagnetic radiation containment systems and devices that facilitate effective and reliable containment of electromagnetic radiation produced by one or more functional modules arranged horizontally and/or vertically in an electronic equipment enclosure. Further, such EMI containment devices and systems should be universal in the sense that the electronic equipment enclosure configuration is independent of the number and type of functional modules employed, and in the sense that physical nature of the contact between adjacent functional modules is substantially the same, regardless of the type, size, number or arrangement of such functional modules disposed in the electronic equipment enclosure.